The present invention relates to a base board for forming an ink-jet head (hereinafter, it may be referred to xe2x80x9cheadxe2x80x9d for simplicity) which prints letters, signs, images, or the like on recording medium such as paper, plastic sheet, fabric, ordinary objects, and the like, by ejecting functional liquid, for example, ink, onto the recording medium. It also relates to an ink-jet head comprising such a base board, a recording unit, for example, an ink-jet pen, comprising an ink storage portion for storing the ink supplied to such an ink-jet head, and an ink-jet apparatus in which such an ink-jet head is installed.
There are various configuration for a recording unit, such as an ink-jet pen, in accordance with the present invention. One of such configurations is a cartridge. A cartridge may comprise an integral or independent combination of an ink-jet head and an ink storing portion. An ink-jet recording unit is structured so that it can be removably mounted on a carrying means, and as a carriage, on the main assembly side of an image forming apparatus.
An ink-jet apparatus with which the present invention is compatible includes a copying apparatus combined with an information reading device or the like, a facsimile apparatus enabled to send or receive information, a machine for printing on fabric, and the like, in addition to an ink-jet apparatus integrated, as an output terminal, with an information processing device such as a word processor, a computer, or the like.
Ink-jet recording apparatuses are distinctive in that they can print highly precise images at a high speed by ejecting ink in the form of a microscopic droplet from orifices. Recently, such ink-jet recording apparatuses that employ electrothermal transducers, which have a portion formed of exothermic resistant material, as a means for generating the energy used for ejecting ink, and that use the bubbling, that is, boiling, or ink caused by the thermal energy generated by the electrothermal transducers, have been attracting attention, because they are particularly suitable for forming high precision images, are capable of recording at a high speed, and make it possible to reduce in size, and/or colorize a recording head as well as a recording apparatus (for example, those disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796).
Generally, a head used for ink-jet recording comprises: a plurality of ejection orifices; a plurality of ink paths leading to the ejection orifices one for one; and a plurality of electrothermal transducers for generating the thermal energy used for ejecting ink. Each electrothermal transducer has an exothermic resistant portion and electrodes, and is coated with electrically insulative film so that it is insulated from the others. Each ink path is connected to a common liquid chamber, at the side opposite to the ejection orifice. In the common liquid chamber, the ink supplied from an ink container as an ink holding portion is stored. After being supplied into the common liquid chamber, ink is led into each of the ink paths, and is retained therein, forming a meniscus adjacent to the outward edge of the ejection orifices. While the head is in this state, the thermal energy generated by selectively driving the electrothermal transducers is used to suddenly heat the ink in contact with the surface of the driven electrothermal transducer to boil the ink. As the ink boils, or the state of the ink changes from liquid to gas, pressure is generated, and ink is ejected by this pressure.
When ink is ejected, the portion of the ink-jet head, which thermally interacts with ink, is subjected to not only the intense heat generated by the exothermic resistant material, but also the shocks (cavitation shocks) caused by the formation and collapsing of ink bubbles. Also, it is chemically affected by the ink itself. In other words, it is subjected to the compound effects of those factors.
Thus, this thermally interactive portion of the ink-jet head is generally covered with a top portion protecting layer for protecting the electrothermal transducer from the cavitation shocks, and also for preventing ink from chemically affecting the electrothermal transducer.
Next, referring to FIG. 3, the generation and collapse of a bubble on the aforementioned thermally interactive portion, and the related matters, will be described in detail.
A curved line (a) in FIG. 3 shows the change in the surface temperature of the top portion protecting layer, which began the moment a voltage Vop (pulse), which was 1.3xc3x97Vth (Vth is the threshold voltage at which ink began boiling) in amplitude, 6 kHz in driving frequency, and 5 xcexcsec in pulse width, was applied to a heat generating member (exothermic resistant member). A curved line (b) in FIG. 3 shows the growth of the generated bubble, which began the moment the voltage was applied to the heat generating member. As the curved line (a) shows, the temperature began to rise after the application of the voltage, and reached its peak slightly after the end of the pulse with a predetermined duration (it took a short time for the heat from the heat generating member to reach the top portion protecting layer). After reaching its peak, it began to fall due to heat dissipation. On the other hand, as shown by the curved line (b), the bubble began to grow when the temperature of the top portion protecting layer reached approximately 300xc2x0 C., and began collapsing after reaching its maximum size. In an actual operation, the above described process was repeated in the head. The surface temperature of the top portion protecting layer reached nearly 600xc2x0 C., for example, as the bubble grew. In other words, it is evident from FIG. 3 how high the level was of the temperature at which ink-jet recording was carried out.
The top portion protecting layer which comes into contact with ink is required to be superior in heat resistance, mechanical strength, chemical stability, oxidization resistance, alkali resistance, and the like properties. As to the material for the top portion protecting layer, precious metals, transition metals with a high melting point, their alloys, nitride, boride, silicide, carbide, amorphous silicon, and the like have been known.
For example, Laid-Open Japanese Patent No. 145158/1990 proposes a recording head superior in durability and reliability, which is realized by placing a top layer formed of Mx (Fe100xe2x88x92yxe2x88x92xNiyCrz)100xe2x88x92x (M stands for one or more elements selected from among Ti, Zr, Hf, Hb, Ta, and W; and x, y and z stand for atom percentages (at. %) in a range of 20-70 at. %, a range of 5-30 at. %, and a range of 10-30 at. %, correspondingly), of the insulative layer which is on the exothermic resistance layer.
In recent years, demands have been increasing for further improvement of an ink-jet recording apparatus in terms of image quality and recording speed, and in order to realize an ink-jet recording apparatus which satisfies these demands, various attempts have been made to improve an ink-jet recording apparatus in many aspects, for example, the head structure, and also to improve the ink itself.
FIG. 2 illustrates an example of the structure of a base board, that is, one of the portions which make up an ink-jet head.
In the base board illustrated in FIG. 2(a), a protective layer 2006 and a top portion protecting layer 2007 are accumulated on an electrothermal transducer which is made up of an exothermic resistance layer 2004 and an electrode layer 2005. The base board illustrated in FIG. 2(b) is a version of the base board illustrated in FIG. 2(a), in which the protective layer has been improved. More specifically, the protective layer of the base board illustrated in FIG. 2(b) has been divided into two sub-layers so that the thermal energy from the exothermic resistant layer 2004 acts more effectively upon ink at a thermally interactive portion 2008. Further, the thickness of the protective layer has been reduced, below the thermally interactive portion 2008. When producing the base board illustrated in FIG. 2(b), first, a first protective sub-layer 2006 is formed of SiO, SiN, or the like, and then, this first protective sub-layer 2006 is removed only from the area, the position of which corresponds to that of the thermally interactive portion in terms of the vertical direction, by patterning or the like. Then, a second protective sub-layer 2002 is formed of SiO, SiN, or the like. As a result, the overall thickness of the protective layer becomes thinner below the thermally interactive portion 2008. Lastly, a top portion protective layer 2007 is formed.
The protective layer on the electrothermal transducer in a base board such as the one described above is required to be electrically insulative, and resistant to ink. It is also required to be resistant to cavitation shocks which occur during ink ejection. If the thickness of the protective layer is substantially increased as shown in FIG. 2(a), the level of the quality which the material for the protective layer requires in terms of the protective performance may be somewhat lowered; in other words, materials which are not perfect for preventing the exothermic resistant layer from being damaged by the cavitation shocks during ink ejection, or from being corroded by ink, can be used as the material for the protective layer. This is due to the fact that the thicker the protective layer, the longer the time necessary for the damage or corrosion to reach the exothermic resistant layer, and therefore, the longer the service life of the head.
Meanwhile, ink has been improved to control bleeding (bleeding between two areas different in color) in order to deal with high speed recording. Ink is also improved in terms of saturation, water resistance, and the like in order to meet the demands for high image quality. Such improvements have been made with the use of additives. When such improved ink, in particular, ink which contains ingredients, such as Ca and Mg, capable of forming bivalent metallic salt, or chelate complex, is used, the protective layer tends to be corroded through a thermochemical reaction which occurs between the protective layer and ink. Increasing the thickness of the protective layer is also effective to extend the service life of an ink-jet head used with such ink.
However, increasing the thickness of the protective layer results in the reduction in the efficiency with which the thermal energy generated in the exothermic resistant layer conducts to the thermally interactive surface.
Thus, the protective layer is reduced in thickness across the area correspondent to the thermally interactive portion as shown in FIG. 2(b), so that the the thermal energy from the exothermic resistant layer 2004 can be more effectively conducted to ink through the second protective sub-layer 2006xe2x80x2 and the top portion protecting layer 2007 to improve thermal efficiency.
However, if the protective layer is reduced in thickness, the damages caused to the thermally interactive portion by the cavitation shock and/or the corrosive effect of ink, reach the exothermic resistant layer more quickly than when the protective layer is not reduced in thickness, although this depends upon the type of the protective layer material. In other words, reducing the thickness of the protective layer is detrimental to the extension of the service life of the head. In particular, when an ink which contains ingredients such as Ca or Mg capable of forming bivalent salts or chelate complexes is used as described above, the above described phenomenon becomes more intense. Thus, when such an ink is used, the material for the protective layer must be far more strictly selected.
In order to further increase the speed of an ink-jet recording, it is necessary to use a driving pulse far shorter in which than the conventional driving pulse; in other words, it is necessary to increase driving frequency. When a driving pulse with such a short width is used, a cyclic of heatingxe2x86x92bubble developmentxe2x86x92bubble collapsexe2x86x92cooling is repeated across the thermally interactive portion of the head at a higher frequency compared to when the conventional pulse is used. In other words, when a driving pulse with such a short width is used, the thermally interactive portion of the head is subjected to thermal stress at a higher frequency. Further, driving the head with a pulse with a shorter width causes the protective layer to be subjected to a greater concentration of cavitation shocks generated by the generation and collapse of bubbles in ink in a shorter time. Therefore, when a driving pulse with the shorter width is used, the protective layer must be far superior in terms of resistance to mechanical shocks.
Although a head structure such as the one illustrated in FIG. 2(b) which employs a thinner protective layer is suitable for driving a head with a pulse with a shorter width, the thinner protective layer is no different from the thicker one in that it is required to be resistant to the cavitation shocks, resistant to ink such as the one described above which has been improved to provide better image quality, and also sufficiently resistant to the thermal stress peculiar to the usage of a driving pulse with a shorter width.
Presently, however, such a protective layer structure that makes it possible for a variety of inks to satisfactorily used, is capable of dealing with a recording speed much higher than the conventional one, and is capable of contributing to the extension of the service life of a recording head, has not been known. When designing a protective layer structure, it is necessary to select the material and structure for the protective layer in consideration of the various features required of a recording head such as the above described features. In terms of the conventional technologies, the problems regarding the corrosive nature of ink have been dealt with by increasing the thickness of the protective layer, and this method is limited where the further improvement in thermal efficiency and further increase in recording speed are concerned (when it comes to the matters of further improving the thermal efficiency and further increasing the recording speed).
The present invention was made in consideration of the above described various problems concerning the protective layer for the thermally interactive portions of a recording head. Thus, the primary object of the present invention is to provide an ink-jet recording head having such a protective layer that is resistant to shocks, heat, and ink, is resistant to acidity, and is highly durable, by solving the above described various problems concerning the protective layer of a conventional ink-jet head, in particular, the portion which makes contact with ink.
Another object of the present invention is to provide an ink-jet base board equipped with such a protective layer that is compatible with the dot size reduction for image improvement in terms of preciseness, and high speed driving for high speed recording, and that lasts a long time regardless of ink choice, and to provide an ink-jet head equipped with such a protective layer, and an ink-jet apparatus equipped with such an ink-jet head.
An ink-jet head base board in accordance with the present invention comprises: a piece of substrate; a plurality of heat generating members placed on the substrate, each of which being disposed between a pair of electrodes; and a top portion protecting layer placed on an insulative layer placed on the plurality of heat generating members.
In this ink-jet head base board, the top portion protecting layer is distinctive in that it is formed of amorphous alloy, the composition of which can be expressed by the following formula (I):
Taxcex1Fexcex2Nixcex3Crxcex4xe2x80x83xe2x80x83(I)
(10 at. %xe2x89xa6xcex1xe2x89xa630 at. %; xcex1+xcex2 less than 80 at. %; xcex1 less than xcex2; xcex4 greater than xcex3; and xcex1+xcex2+xcex3+xcex4=100 at. %)
and also in that it contains the oxides of its compositional components, at least in the portion next to its surface which comes in contact with ink.
Also, an ink-jet head in accordance with the present invention comprises: a plurality of orifices through which liquid is ejected; a plurality of liquid paths which are connected to the plurality of orifices one for one, and have a portion across which the thermal energy for ejecting the liquid is caused to act on the liquid; a plurality of heat generating members for generating the thermal energy; and the top portion protecting layer which covers the plurality of heat generating members, with the interposition of an insulative layer.
In this ink-jet head, the top portion protecting layer is distinctive in that it is formed of amorphous alloy, the composition of which can be expressed by the following formula (I):
xe2x80x83Taxcex1Fexcex2Nixcex3Crxcex4xe2x80x83xe2x80x83(I)
(10 at. %xe2x89xa6xcex1xe2x89xa630 at. %; xcex1+xcex2 less than 80 at. %; xcex1 less than xcex2; xcex4 greater than xcex3; and xcex1+xcex2+xcex4+=100 at. %)
and also that the surface of the top portion protecting layer, which comes into contact with ink, contains the oxides of its compositional components.
Further, the ink-jet recording unit in accordance with the present invention is distinctive in that it has an ink-jet head structured as described above, and an ink storage portion in which the ink to be supplied to such an ink-jet head is stored.
Further, an ink-jet apparatus in accordance with the present invention is distinctive in that it has an ink-jet head or an ink-jet recording unit, which is structured as described above, and a carriage for moving such an ink-jet head or an ink-jet recording unit, in accordance with recording information.
Further, one of the methods for manufacturing an ink-jet head base board in accordance with the present invention is characterized in that the top portion protecting layer of an ink-jet head base board structured as described above is formed by using a method of sputtering which uses a target formed of metallic alloy containing Ta, Fe, Cr and Ni in a manner to satisfy the above compositional formula, or Formula (I).
Another method for manufacturing an ink-jet head base board in accordance with the present invention is characterized in that the top portion protecting layer of an ink-jet head base board structured as described above is formed by using a method of double element sputtering which uses both a target formed of metallic alloy containing Ta, Fe, Cr and Ni in a manner to satisfy the above compositional formula (I), and a target formed of Ta.
According to one of many aspects of the present invention, even when various inks different in properties are used, the top portion protecting layer, which makes contact with ink, is not corroded, and therefore, it is possible to provide an ink-jet head which has a protective layer superior in shock resistance, heat resistance, ink resistance, and oxidization resistance. The present invention is applicable to an ink-jet head base board provided with a protective layer which lasts a long time in spite of the dot size reduction for the image improvement in terms of preciseness, and the high speed driving for high speed recording. Further, the present invention is also applicable to an ink-jet head unit for an ink-jet apparatus, which comprises an ink storage portion for storing the ink to be supplied to the above described superior ink-jet recording head, as well as an ink-jet apparatus in which such an ink-jet head is installed.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.